I may have missed it; I didn’t see any discussion about side effects experienced after the first dose.

If patients had previously experienced negative side effects after the first dose, it seems this would prime them for hesitancy leading up to their second Pfizer vaccination dose (which is when the hesitancy was measured).
e: to clarify, patients who experienced negative effects after the first dose would be more likely to have negative symptoms after subsequent doses and would be primed with hesitancy and so that could produce the results above. If I missed something though happy to be corrected.

Aside from that issue, though, this seems to have big implications for the public reporting databases as well - eg VAERS may overestimate vaccine side effects because many patients are actually experiencing Nocebo effects instead due to the prevalence of misinformation.